Companding or Compandsion

Companding (compression and expansion of transfer data) can be found in many different
applications, especially in digital telephone systems. A digital telephone system converts an
analog speech signal to a digital signal. This digital signal is referred to as linear—meaning
without compression. Instead of transmitting this linear digital signal across the telephone
network, this digital signal is usually first compressed before being transmitted to reduce the
transmission bandwidth. The receiver needs to expand this non-linear, compressed signal back
to a linear digital signal. Companding refers to this combined process of compression and
expansion.
Two companding format for G.711 Audio are a law and u law.

SoX raw audio data converter. wav to/from mulaw

Utility SoX (Sound Exchange)

Convert mulaw to wav:
    sox.exe -t ul input_mulaw_file output_wav_file


Convert wav to mulaw:
    sox.exe input_wav_file -r 8000 -c 1 -t ul output_mulaw_file